1. Field of the Invention
The present invention relates to manufacturing of semiconductor integrated circuits.
2. Discussion of the Background
Manufacturers of semiconductor integrated circuits are faced with intense competitive pressure to improve their products and processes used to fabricate the products. The manufacturers have a large business motivation to lower production costs by improving product throughput, quality and complexity. Additionally, manufacturers have a need for repeatability and consistency in the assembly and functioning of semiconductor fabrication equipment. Accordingly, semiconductor manufacturers strive to formulate a low cost way to manufacture high quality process equipment.
One goal of semiconductor manufacturers is to improve tool performance at a low cost. Another goal is to make process equipment function the same regardless of particular hardware sampled. The company that can enhance tool performance without increasing tool cost is in a position to increase profit margins. In cyclical industries such as the semiconductor capital equipment industry, increased profit margins can have a dramatic impact on market penetration.
For many years Inductively Coupled Plasma (ICP) sources have been used in a variety of applications. Most recently, low pressure (<100 mTorr) ICP sources have been used in wafer production where plasmas are required to deliver high densities of ions, electrons and radicals with high uniformity over wafer diameters of 200 mm and larger. These plasma sources need to deliver ions that are uniform in density and energy distribution while keeping ion and electron energy very low.
The Electrostatically Shielded Radio Frequency (ESRF) plasma source is a type of ICP source which is particularly useful in applications where substrate materials are susceptible to damage from high energy plasma ions or electrons, uncontrolled bias voltages and thermal fluxes. ESRF sources feature pure inductive coupling with reduced capacitive coupling. The radio frequency (RF) power produces only plasma density and induces very little voltage on the plasma. This inductive coupling is sufficiently devoid of capacitive coupling so that the plasma does not search for counter electrodes. The plasma remains mainly within the process (dielectric) chamber at all powers and pressures.
The main components of an ESRF ICP processing system are depicted in the generic FIG. 1. The ESRF ICP processing system 10 includes a process chamber 20 with a wafer and chuck assembly 30 provided therein. A gas inject assembly 40 is provided opposite the wafer and chuck assembly 30. A plasma region or area 22 is provided adjacent a dielectric chamber wall 60 in between the wafer and chuck assembly 30 and the gas inject assembly 40.
The plasma source is composed of several main elements and is affixed to an opening of a suitable process chamber 20. A wafer that is being processed is located on the chuck assembly 30. The plasma source comprises a resonator chamber or cavity 72 bounded by an outer shield or housing 50 and the dielectric chamber wall 60, within which a helical coil 90 is mounted. The outer shield 50 and the dielectric chamber wall 60 further define a fluid cooling area 70, within which the helical coil 90 is immersed. The dielectric chamber wall 60 contains the plasma area 22 of the plasma source. Furthermore, the dielectric chamber wall 60 has appropriate sealing devices to seal cooling fluid within fluid cooling area 70 and maintain the process pressure within plasma area 22 at appropriate levels. Additionally, an electrostatic shield 80 is provided on an outer surface of the dielectric chamber wall 60 in an interior of the fluid cooling area 70.
In the construction of ESRF source assemblies, there are several elements that are expensive to fabricate for various reasons. The outer shield or housing can be the most expensive part in the source. It can be fabricated from several aluminum parts and subsequently furnace or dip brazed to form a singular assembly. The interface of these parts must be machined to tolerances required in the brazing process. Once machined, the parts are then assembled utilizing an appropriate holding fixture and brazed using the specified processes. Various machining operations must then be performed on the resulting brazed assembly before it is ready for use.
Another problem seen in ESRF plasma sources is the method and repeatability of mounting the helical coil. In ESRF plasma sources, particularly those sources comprising a quarter-wave or half-wave resonant coil, the coil is tuned to a particular frequency. In order to tune the helical coil to a particular frequency, a labor intensive process of adjusting the length of the coil is involved. Once the coil is tuned, changes in coil position can adversely affect the tuning.